Furlable antenna



N. BARBANO ET AL March 10;- 1970 FUBLABLE ANTENNA 3 Sheets-Sheet 1 Filed Nov. 30, 196'? AGENT ATTORNEY March 10, 1970 BARBANO ETAL 3,500,424

- FURLABLE ANTENNA Filed Nov. 30, 1967 v 3 Sheets-Sheet 2 3| INVENTORS NORMAND BARBANO DONALD L. JOHNSTONE BY )M N WW ATTORNEY AGENT March 10,1970 NBARBANO ETAL 7 3,500,424

FURLABLE ANTENNA Filed Nov. 30, 1967 3 Sheets-Sheet 5 I NV EN TORS NORMAND BARBANO DONALD L. JOHNSTONE ATTORNEY AGENT United States Patent O US. Cl. 343-7925 Claims ABSTRACT OF THE DISCLOSURE Planar conductive patterns comprising dipole radiating elements and feed lines of the antenna are formed by printed circuit techniques on the same side of a flexible nylon sheet. The feed lines have trapezoidal Wave-like configurations centered about the longitudinal axis of the antenna and physically displaced relative to each other as though the waves are 180 electrical degrees out of phase with each other. In other words, each feed line has a longitudinal series of straight sections parallel to and successively positioned on opposite sides of the axis with the successive sections electrically interconnected. The straight sections of the feed lines on the same side of the axis are axially aligned and spaced. One of its feed lines is discontinuous between successive sections thereof, and the other is electrically continuous. A flexible coaxial cable extends the length of the antenna and is electrically connected to and aligned with each of the straight sections of the discontinuous feed line. The center conductor of the coaxial cable is connected to the continuous feed line at the feed point of the antenna. The halves of each tions of the respective feed lines.

BACKGROUND OF THE INVENTION This invention relates to antennas and more particularly to an improved furlable dipole antenna array. A furlable antenna is defined as an antenna that can be wrapped, rolled or folded into a conveniently transportable or storageable package that has substantially less surface area than the erected antenna.

Many low frequency radio frequency communication systems have field applications which involve transporting the system to and from remote locations. In some instances, these communication systems must be transportable by man or beast to the operational site. For a VHF communication system, for example, the antenna dimensions reach bulky proportions, and accordingly the antenna must be capable of being dismantled or otherwise packaged into a small volume suitable for transportation.

The difficulty with antennas having detachable parts or elements is the time required to disassemble or reassemble multielement arrays. Also, these multielement arrays if made from standard rod or similar conductor elements are heavy and bulky even in the disassembled condition.

The general object of this invention is the provision of a furlable VHF antenna which may be packaged in a conveniently small volume for transportation or storage.

SUMMARY OF THE INVENTION In accordance with this invention, strip conductors comprising the active antenna elements and directly connected feed lines are formed on flexible sheet material so that this entire sheet assembly may be folded, rolled or wrapped without damaging the conductors. A coaxial cable coextensive with the antenna has its outer conductor connected to one of the strip feed lines at several longitudinally spaced points and its center conductor connected to the end of the other strip feed line. The coaxial lineis adapted to be rolled without damage into a coil when ,the antenna is compacted for storage.

BRIEF DESCRIPTION OF DRAWINGS FIGURE 1 is a plan view of a log periodic antenna embodying the invention;

FIGURE 2 is an enlarged fragmentary view of the high frequency end (the right side, as viewed in FIGURE 1) of'fthe central or feed portion of the antenna shown in FIGURE 1;

FIGURE 3 is an enlarged fragmentary view of the low frequency end (the left side, as viewed in FIGURE 1) of thecentral or feed portion of the antenna shown in FIGURE 1;

FIGURE 4 is a section taken on line 44 of FIGURE FIGURE 5 is a section taken on line 5-5 of FIGURE 2; and

FIGURE 6 is a transverse section taken on line 66 of FIGURE 2.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, a preferred embodimentof the invention is shown in FIGURE 1 as a log periodic antenna 10 having a plurality of dipoles 16-26, inclusive, extending from and connected to a central feed assembly 31. The dipoles and feed assembly comprise strip conductors and are secured to and supported on a flexible dielectric sheet 32, preferably vinyl impregnated nylon. Mounting holes 33 at the corners of sheet 32 permit convenient support of the antenna in its unfurled operative position. This antenna is shown in FIGURE 1 in its operating or unfurled state and may be furled for transportation by successively folding the antenna about fold lines 3540, inclusive, and thereafter rolling or folding the folded assembly on itself about an exis transverse to the antenna axis.

The dipole elements preferably are conductive strips 43, see element 16 in FIGURE 3, approximately 0.001 inch thick and formed on a thin flexible dielectric sheet 44 such as vinyl impregnated nylon approximately 0.002 inch thick. In practice, conductive strips mounted on the dielectric sheet are available commercially and may be formed by conventional printed circuit techniques or cut to length and width as required for the making of the antenna. These elements are connected at their inner ends to the central feed assembly which is energized by a coaxial line 45 connecting the assembly to utilization apparatus U such as a transmitter or receiver.

The central feed assembly 31 comprises a pair of strip feed lines 46 and 47 (see FIGURES 2 and 3) formed on a flexible dielectric sheet 48 preferably by photoetching or similar precision printed circuit technique. Each feed line includes a plurality of tabs 49 for facilitating connection of dipole elements to the feed lines.

Line 46 is a continuous conductor throughout the length of the antenna and is electrically connected to the halves of successive dipoles on opposite sides of the antenna axis. More specifically, line 46 is connected to alternate even numbered dipole elements (i.e., 16a, 18a, etc.) on one side of the antenna and to alternate odd numbered elements (i.e., 17b, 19b, etc.) on the opposite side of the antenna. Line 46 crosses the axis of the antenna approximately midway between adjacent elements to effect a phase reversal of the feed between adjacent elements as required for operation of the antenna. The portions or sections 46' of line 46 between the crossover points are straight and parallel to the axis of the antenna. Feed line 47 comprises straight conductor sections 47 laterally spaced from conductor section 46 by a precisely controlled distance B which determines the impedance of the antenna. Adjacent strip sections 47 are separated or spaced from each other at the crossover point of line 46 and therefore the strip conductors 47 comprising line 47 are longitudinally discontinuous. Line 47 is electrically connected to the remaining halves of successive dipoles on opposite sides of the antenna axis.

In accordance with the invention, coaxial line 45 is mounted on and aligned with the strips 47 of line 47. The outer conductor 45a of the coaxial line is electrically connected at longitudinally spaced intervals indicated by Xs in FIGURES 2and 3 to provide electrical continuity for line 47 throughout the length of the antenna. The coaxial line has a serpentine configuration as viewed in FIGURES 1, 2 and 3 and crosses the axis of the antenna at the crossover point between adjacent dipole elements. The portion of the coaxial line between electrical connections to the strips 47 are unsecured and therefore free to flex laterally in the plane of the feed assembly when the antenna is folded.

The feed point P of the antenna is located at the high frequency (smallest) element of the antenna as shown at the right in FIGURE 2. Coaxial line 45 extends the full length of the antenna from the low frequency end thereof in the criss-cross manner described above to the feed point P. Center conductor 45b of this line is connected directly to the end 46" of feed line 46 at this feed point P. Thus the antenna with its balanced feed is energized directly by an unbalanced line without a matching network, transformer or similar frequency limiting component. As illustrated in FIGURE 2 and the section views of FIG- URES 5 and 6, outer conductor 45a of coaxial line 45, and thus feed line 47 is electrically isolated from the feed line 46 at the crossover points by a dielectric spacer 52, such as Teflon made by E. I. du Pont de Nemours & Co. The dimensions and dielectric constant of spacer 52 are selected so that the impedance of the line remains constant even at the crossover points of the two feed lines.

The conductive patterns 46 and 47 comprising the central feed assembly 31 are formed by conventional printed circuit techniques on a flexible copper clad dielectric sheet 48 such as Kapton, manufactured by E. I. du Pont de Nemours & Co. The copper clad conductive patterns 46 and 47 are typically 0.0015 inch thick. The Kapton backing material is typically 0.002 inch thick. The width A of the conductive patterns 46 and 47 (see FIGURE 2) and the spacing B therebetween are typically 05' inch and 0.02 inch, respectively, and are selected such that the antenna feed has the desired characteristic impedance. Similarly, the dipole elements 16 to 26 are formed by conventional printed circuit techniques from a copper clad flexible nylon sheet such that the width C of the dielectric sheet 44 (see FIGURE 2, dipole element 24a) is greater than the width D of the conductive element 43 which is equal to the width of the tabs 49 of the conductive patterns. A portion of dielectric sheet 44 is removed at one end of the dipole elements to expose a length of the conductor 43. The exposed portion of the conductor 43 is then located over the tab of an associated feed line (e.g., tab 49" and line section 47") and low temperature resistance soldered or welded thereto.

The antenna structure is assembled by bonding the dielectric sheet 48 and conductive elements 43 of the dipole elements to the vinyl impregnated nylon sheet 32 with a bonding agent such as rubber adhesive 2141 manufactured by Minnesota Mining and Manufacturing Company. The central feed assembly 31 is oriented so that the feed lines are facing away from sheet 32. The dipole elements, however, are oriented so that the conductive elements 43 are facing sheet 32. In order to support the ends of dipole elements 43 and prevent the bond between tabs 49 and the dipole elements breaking when the antenna is furled, a

thin flexible layer 53 of flexible epoxy is formed over the junction of the dipole elements and the central feed assembly. Alternatively, tapered layers of Mylar, manufactured by E. I. du Pont de Nemours & Co., may be formed over the junctions of the tabs and dipoles. A thin flexible sheet 54 of vinyl impregnated nylon is then placed and stretched over the antenna. The dielectric sheets 32 and 54 are then bonded together by heat sealing immediately adjacent the dipole elements and central feed assembly. Excess or loose portions of sheet 54 between the dipole elements are cut from the antenna.

By way of example, a furlable log periodic dipole antenna embodying this invention and successfully operating over the frequency band mHZ. to 250 mHz. had the following dimensions:

Dipoles 1626: Inches Dimension C 1.0 Dimension D 0.5

Central feed assembly 31:

Lines 46 and 47:

Thickness 0.0015 Dimension A 0.75 Spacing B 0.020

Sheet 48:

Length 32.0 Width 2.52 Thickness 0.002

Coaxial line 45:

Outer diameter 0.025

Spacer 52:

Length 0.50 Width 0.25 Thickness 0.005 Material-Teflon.

Relative dielectric constant 2.1

Sheet 32:

Length 33.0 Width 73.8 Thickness 0.002

Sheet 54:

Thickness 0.002

Overall dimensions:

Length 33.0 Width 73.8

Furled dimensions:

Length 20.0 Width 12.0 Thickness 4.0

Changes, modifications and improvements may be made to the above described preferred embodiment of the invention without departing from the spirit of the invention. For example, the feed lines and dipole elements may be simultaneously formed on the same copper clad dielectric sheet if printed circuit facilities are available for accommodating such a large item. The scope of the claims define the advance the invention makes in the art.

What is claimed is:

1. A planar dipole antenna array having a longitudinal axis comprising:

a flexible sheet of dielectric material,

a continuous conductor having a series of electrically connected sections arranged with adjacent sections on opposite sides of the longitudinal axis of the antenna,

a discontinuous conductor having a series of longitudinally spaced segments arranged with adjacent segments on opposite sides of said antenna axis,

said conductors being so relatively positioned that a conductor section is transversely aligned with and on the opposite side of the axis from a conductor segment,

first means for securing said conductors to one side of said flexible sheet,

a flexible coaxial transmission line having successive lengths located alternately on opposite sides of said longitudinal axis, each of said lengths being adjacent to a segment of said discontinuous conductor, said coaxial line having an inner and an outer conductor,

first means for electrically connecting said outer conductor to each of said segments,

means for electrically insulating said outer conductor from said continuous conductor, and

second means for electrically connecting said inner conductor to the continuous conductor at one end of the antenna.

2. The antenna according to claim 1 including a plurality of longitudinally spaced transversely extending antenna elements on opposite sides of said aXis,

longitudinally adjacent elements on each side of said axis being electrically connected to a segment and a section, respectively, of said conductors.

3. The antenna according to claim 2 wherein said segments and sections are parallel to the longitudinal axis of the antenna.

4. The antenna according to claim 3 wherein said outer conductor is electrically connected to said segments at longitudinally spaced intervals whereby the coaxial line therebetween is free to flex when the antenna is furled.

5. The antenna according to claim 4 wherein said first securing means comprises:

a second flexible sheet of dielectric material,

said continuous and discontinuous conductors being formed on said second dielectric sheet by printed circuit techniques, and

second means for securing said second dielectric sheet and said antenna elements to said first dielectric sheet.

References Cited UNITED STATES PATENTS 3,108,280 10/1963 Mayes et al. 343-7925 US. Cl. X.R. 343-814, 881 

